The Small Computer System Interface (SCSI) is a parallel input/output bus often used to connect disk drives, CD-ROMs, tape drives and other peripherals to a computer bus. The SCSI bus is a bi-directional multimaster bus which can accommodate peer to peer communications along multiple CPU's and multiple peripherals. Because of its versatility, the SCSI interface has become increasingly important in the microcomputer field.
A SCSI bus must be terminated at both ends of the bus. Consequently, for an SCSI interface controller with multiple ports, it is necessary to determine if that controller constitutes an end of the bus. If the controller does comprise one end of the SCSI bus, then it must be terminated. For example, if a controller has two ports, both of which have devices attached thereby placing the controller in the middle of the bus, then no termination at the controller is required. If however, one port or the other is vacant, then the controller by definition is one end of the SCSI bus therefore requiring termination.
In response to this problem, there have been developed several methods for providing suitable termination of unoccupied SCSI ports. However, all of the methods previously used, involve manual intervention when termination is desired. This manual intervention generally requires an operator to attach a jumper or set of jumpers which enable a termination circuit which prevents the unconnected lines from hindering the SCSI's operation. Then, in order to disable the termination circuit, the jumper or jumpers need to be removed manually by the operator.
Hence, it would be desirable for a SCSI interface to provide for automatic termination to be applied to SCSI ports which are not presently in use. Such automatic termination would increase the ease of use of SCSI ports and corresponding flexibility and versatility, in that when a device was to be connected or disconnected, the operator could simply attach or remove the corresponding device from the SCSI port without need for additional manual intervention with respect to termination enabling or disabling. An automatic termination circuit would also eliminate a source of SCSI malfunction in that the automatic termination circuit would enable or disable termination as necessary and eliminate the possibility of human error.
Finally, an automatic termination circuit would eliminate the need for either resistor packs or jumpers and, therefore, eliminate physical manipulation and increase the useful life of interconnectors.